• Next Boot: Detect fans added to the motherboard upon next boot only.
• Disabled: Will not detect fans added to the motherboard, new fans may perform erratically.
• Always: Detect fans added to the motherboard (may cause a slight delay and increased noise during startup).

See "BIOS Beep Codes" in the Quick Reference section of Webopedia.
Also see "The System Boot Process Explained" in Webopedia's Did You Know...? section.

Intel Desktop Boards BIOS Settings (PDF)
The BIOS Setup program can be used to view and change the BIOS settings for the computer.

Intel Desktop Boards BIOS Settings Menus (PDF)
The presence of menus and BIOS settings are dependent on your board model, hardware components installed, and the BIOS version. BIOS menu titles may differ.

Webopedia Did You Know - From AT to BTX: Motherboard Form Factors
You've probably heard the term motherboard a thousand times, but do you know what it really means and how it relates to the rest of your computer?

What You Need to Know About Motherboards
You can think of the motherboard as a communications center. The purpose of the motherboard is to provide the means for all the other components and peripherals to talk to each other.